These studies are directed at two aspects of control of the circulation: 1) Regulation of cerebral blood flow; 2) Regulation of flow through vasa vasorum of the aorta. During the past year, studies concerned: 1) Effects of putative neurotransmitters acetylcholine and vasoactive intestinal peptide, on cerebral blood flow; 2) Role of sympathetic nerves in regulation of cerebral blood flow at physiological levels of arterial pressure; 3) Blood flow through aortic vasa vasorum in atherosclerotic monkeys; 4) Development of a method for on-line measurement of cerebral blood flow. Research goals for the coming year are to answer these questions: 1) Does stimulation or interruption of the greater superficial petrosal nerve, which provides cholinergic fibers to cerebral vessels, alter cerebral blood flow? 2) Does sympathetic denervation increase cerebral blood flow or disruption of the blood-brain barrier in unanesthetized, acutely hypertensive cats and rats? 3) Does acute hypoxia alter the proportion of nourishment to arterial walls by diffusion from the lumen and from vasa vasorum?